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Evaluate Corn Rootworm Pressure this Season

February 18, 2013
By: Rhonda Brooks, Farm Journal Seeds & Production Editor
Westerncornrootworm interior

Fields with a high level of corn rootworm pressure can benefit from soil insecticides. If you’re unsure, try one of these two methods of assessment the Burrus Seed Company recommends.

Root dig method

  1. Walk fields in July and August; record observations on rootworm beetle populations.
  2. Dig roots in July and August to evaluate rootworm control in traited and refuge acres.
  3. If the rootworm beetle population is high and root ratings of rootworm-traited hybrids are .25 or higher in the field, use a granular soil insecticide next year.


Rootworm beetle count method

  1. Scout rootworm-traited acres at pollination.
  2. Examine four consecutive plants in five areas of the field. Start at the base of the plant and count beetles on leaf surfaces, leaf axils, stalk, ear tip, and tassel.
  3. Determine the average number of beetles per plant.
  4. If the average rootworm beetle population is at least .75 beetles per plant, consider using a soil insecticide with rootworm-traited corn the next year.
  5. If the rootworm population is less than .75 beetles per plant, wait two weeks and scout again. When the beetle population remains low for six weeks after the first scouting trip, no soil insecticide is necessary with rootworm traits.

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